ASoC: SOF: mediatek: add shutdown callback

If we do not shutdown the peripheral properly at shutdown, the whole system
crashes after kexec() on the first io access.

Let's implement the appropriate callback.

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20221127-mtk-snd-v1-0-b7886faa612b@chromium.org


Signed-off-by: Mark Brown <broonie@kernel.org>